It’s time for a new RAN architecture

We’re in the midst of exciting and challenging times for mobile infrastructure providers. On one hand, there’s more demand than ever before, every application ever imagined is or will be operating on the mobile network and there’s no end in sight to the possibilities to utilize next generation mobile technology. On the other hand, the current RAN architecture hasn’t kept pace, becoming a barrier to operational efficiency and innovation. It’s time for a new RAN architecture.

Sachin Katti

xRAN.org is a consortium of top tier operators and radio access network equipment vendors whose goal is to develop a modular architecture for the cellular radio access network. The architecture aims to develop standardized north and south bound interfaces to quickly deploy services, enable implementation of RAN software on COTS hardware and provide flexibility in placing the software functions at the edge or at the cell site depending on fronthaul availability.

Why xRAN? Traditional radio access network architectures are ill-suited to meet the requirements of today’s carriers and end-users. Radio access network infrastructure is proprietary, expensive to scale, hard to program, and cumbersome to introduce new business applications beyond connectivity. On the demand side, traffic is growing exponentially and becoming increasingly diverse. The traffic mix will be diverse, ranging from voice, data and video to new applications such as smart grids, drones and automotive applications. Each one of these classes will have distinct QoS expectations of the network. However, on the supply side, available spectrum and spectral efficiency (i.e. the maximum throughput achievable per Hz of spectrum) are flattening out. In fact, the spectral efficiency of 4GLTE PHY is fairly close to (within 20% of) the Shannon capacity limit, and further improvements are likely very expensive to implement and will only provide limited gains.

Why now? To deal with these challenges, future wireless networks have to change in two fundamental ways. First, network deployments have to get dense and tightly coordinated. Second, since there is no one-size-fits-all network stack, networks have to dynamically adapt to meet the distinct requirements of diverse applications. They will have to dynamically switch between providing low latency connectivity for automotive applications, to predictable high throughput connectivity for video, persistent reliable connectivity for data, etc.

However, current radio access network architectures are ill-equipped to support a dense and application driven wireless infrastructure. First, current networks are hard to program, network stack software is realized in a tightly coupled fashion on proprietary hardware and its quite difficult to adapt to the requirements of new applications. Second, since it will be impossible to obtain regularly placed cell sites for an infrastructure with much higher density, base stations will be deployed wherever possible in a chaotic fashion. However, a chaotic and dense wireless deployment will be very complex to manage, since it will experience highly variable loads and unpredictable inter-cell interference among other things. Finally, a dense infrastructure is very expensive to deploy and operate. Due to the proprietary and diverse nature of the HW and SW platforms used to build base stations, economies of scale that have been available in other networking domains such as datacenters are not possible in the RAN. Further, there is very little vendor interoperability, limiting operator choice and therefore increasing costs.

With this initiative we propose to decouple the control and user planes in the RAN, standardize the user plane silicon and software with open interfaces, and logically centralize network intelligence and state and abstract the underlying network infrastructure from business applications. The xRAN architecture will build a reference system for LTE-A, with an eventual goal of defining and building the same architecture for 5G once the new air interface is finalized. As a result of this architecture, carriers will gain unprecedented programmability on the RAN, automation and network control, a supply chain of off-the-shelf components to build out their mobile access network; enabling them to build highly scalable, flexible radio access networks that they can rapidly adapt to changing business and traffic needs.

xRAN promises to deliver substantial benefits to carriers and their network subscribers, including:

Several fold increase in spectral efficiency through co-ordinated radio resource control to exploit interference;

Rapid innovation with the ability to deliver new capabilities without configuring individual devices or wait for vendor releases;

Increased value of carrier network, beyond connectivity, by applying intelligent services and control in the network;

Tight alignment with carrier edge cloud infrastructure to allow dynamic orchestration of compute and storage with mobile network; and

About the author:Sachin Katti is a Professor of Electrical Engineering and Computer Science at Stanford University. He is helping lead the xRAN consortium in developing future RAN architectures and reference implementations. Previously Sachin founded Kumu Networks which commercialized his research on full duplex radios.